If you have a heavier door that weighs more than 150 pounds with one spring still wound you will need to use 2 scales and position them under the first row of hinges from each end of the garage door.
How much wight garage door.
How much weight can a garage door opener lift.
Like many other motors garage door openers are rated with horsepower hp or horsepower similar hps for dc motors.
A standard 25 steel gauge 8 x 7 residential garage door from unique raynor amarr haas.
Based on this rating a 1 2 hp opener be able to lift about 185 pounds and a 3 4 hp opener should be able to lift over 370 pounds.
Garage door weight is determined by size material steel gauge thickness insulation and glass.
It should be noted that since the cable loops around a pulley the lifting force of a 210 pound spring is only 105 pounds as seen by the garage door.